Stem for use in joint arthroplasty

ABSTRACT

The invention relates to a prosthesis for implantation into a long bone during joint arthroplasty, particularly Total Shoulder Arthoplasty and Total Hip Arthroplasty, and a method for use of the implant.

PRIORITY CLAIM

This application is a continuation of U.S. patent application Ser. No.13/308,221 filed Nov. 30, 2011, which in turn claims priority under 35U.S.C. §119(e) to U.S. Provisional Application No. 61/418,346, filed onNov. 30, 2010; the entireties of each of the aforementioned priorityapplications of which are incorporated by reference herein and made apart of the present specification.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to, in some aspects, the geometry of a stem forimplantation within long bones during joint arthroplasty, particularlyas it relates to Total Hip Arthroplasty or Total Shoulder Arthroplasty.

Description of the Related Art

Total joint arthroplasty is an established surgical treatment ofdiseased joints and is effective in the relief of pain and therestoration of function of disease compromised joints. Successful jointarthroplasty results in the restoration of functionality, mobility, andquality of life to patients who would otherwise be disabled as a resultof joint disease.

A typical surgical procedure involves the surgical exposure of theaffected joint, resection and excision of diseased bone tissue and thereplacement of the excised tissue with a manufactured, mechanical jointset. The joint components may be attached to native bone by means ofconventional fasteners, bone cements or interference fitting of thecomponents within prepared cavities in the native bone structure.

A typical joint set comprises a rigid stem placed within the medullarycanal of the long bone of the joint, typically manufactured fromstainless steel, titanium, chromium cobalt alloy or other bio-compatiblemetal, a generally spherical or convex articulating component, typicallymanufactured of a metallic alloy or ceramic material and a correspondingconcave articulating surface, typically manufactured from a polymer orceramic material.

Exposure of the joint structure may be accomplished by a surgicalapproach which is directed posteriorly or by an approach which isdirected anteriorly to the femur or humerus. In hip surgery theposterior approach is currently used by many surgeons as it allows for awide exposure of the bone structures and good visualization within thewound. In shoulder surgery an anterior approach is typical. In manyinstances the surgical approach is dictated by the size and geometry ofthe implant devices being used. The current approaches typically resultin a large incision size with associated muscle dissection and may bedisruptive to patient anatomy. Recently, various minimally invasivetechniques have been developed which require smaller incision sizes. Ananterior approach to the hip joint structure has been developed andattempts are being made to minimize the incision and exposure of theshoulder joint. Associated with these techniques is a reduced exposureof, and access to, the bones within the joint structure. In addition,the reduced exposure and access pose substantial challenges to thesurgeon as they relate to resecting diseases of the bone, preparing thenative bone to receive implant devices, and inserting many of theimplant devices currently available. The degree of difficulty associatedis often higher, can result in higher complication rates when comparedto conventional procedures with larger surgical exposures, and mayrequire extended surgery times. Further, surgical outcomes are varied,depending upon surgeon skill and the nature of the defects in the nativebone. As a consequence there is a need for implant components,particularly long bone implant components, which are compatible withsmaller incisions and more restricted access to the native bone.

A further consequence of the small exposure is the limited spaceavailable to the surgeon within the joint wherein inter-operativeadjustment of implant position can be made.

The axial position of the stem within the femoral or humeral bone is ofparticular importance. Misalignment of the stem with respect to thenatural axis of the bone (known as varus and valgus mal-alignment) canresult in abnormal biomechanics of the joint and atypical stressdistributions within the bone structure which may result in implantloosening, dislocation, pain, or may cause fractures of the bone.Mal-alignments may result from poor surgical technique, inadequateexposure of the femur, incompatibility of instruments and implants withthe surgical approach, or from natural deformities of the native bonewithin the medullary canal or metaphyseal regions of the bone.

Mal-alignment of the implanted stem may result in aseptic loosening ofthe implant or localized remodeling of the native cortical bone overtime, ultimately causing failure of the implant and requiring additionalrevision surgeries to be performed to repair or replace the implant.These problems are well described and discussed in the publishedliterature, including but not limited to, Panisello et al., (Journal ofOrthopedic Surgery; 2006 April; 14(1): 32-37), Braun et al.(OrthoSupersite; October 2007), Ozturk et al. (Jun. 3, 2010), U.S.Patent Pub. No. 2004/0107002 to Katsuya, U.S. Patent Pub. No.2008/0091274 to Murphy, U.S. Pat. No. 5,314,489 to Hoffman et al., andU.S. Pat. No. 5,514,184 to Doi et al., the descriptions of the clinicalissues associated with stem alignment, biomechanics and implant failurebeing incorporated herein by reference in their entireties.

The aforementioned patents, publications, and articles incorporated byreference contain therein various designs and methods directed ataddressing the previously discussed issues.

Various embodiments of implant stems have been described in the priorart in an attempt to resolve the issues previously described. Certainconventional stems have a proximal portion designed to locate within themetaphysis of the femur or of the humerus and a distal portion disposedto be located within the medullary canal of the bone. The proximalportions of these stems are either generally cylindrical or rectilinear(rectangular, triangular or trapezoidal) in shape when viewed in crosssection along the proximal to distal axis of the implant and areintended to generally fill the metaphyseal region of the bone, thedistal portion of each embodiment being narrow forms and being elongatedso as to fit within the intramedullary canal of the distal region bone.

In general, the design of currently available implant stems involves theaxial cross sections of the implant along the axis from the proximalportion to the distal end wherein the cross sectional profile isconstant but the cross sectional area of the implant taken in a planesubstantially perpendicular to the longitudinal axis reduces from theproximal to distal end.

Further, the cross sections are generally wider at the medial side thanat the lateral side all along the axis of the implant. The distalportions of some implants may be cylindrical and may incorporate avariety of features including protrusions or secondary components inorder to center the distal portion within the medullary canal and aidwith implant alignment and fixation.

Disclosed herein is a novel design for a stem to be used within longbones during joint repair surgery.

SUMMARY OF THE INVENTION

There is provided in accordance with some embodiments a long boneimplant for use in joint arthroplasty comprising a first end, a secondend comprising a blunt tip, and a stem of the implant disposed betweenthe first and second ends, such that a proximal portion of the stemcomprises an anterior surface, a posterior surface, a medial surface anda lateral surface, wherein a measure of said medial surface taken in aplane perpendicular to the longitudinal axis of the implant is greaterthan a measure of said lateral surface taken in the same plane and adistal portion of the stem comprises an anterior surface, a posteriorsurface, a medial surface, and a lateral surface wherein a measure ofsaid lateral surface taken in a plane perpendicular to the longitudinalaxis of the implant is greater than a measure of the medial surfacetaken in the same plane.

In some embodiments, in the proximal portion of the stem, the medialsurface dimension or measure (e.g., a transverse dimension) taken in afirst plane perpendicular to the longitudinal axis of the implantcomprises a dimension or measure 5% to 100%, or more, greater than thelateral surface measure in the same plane and, in the distal portion ofthe stem, the lateral surface taken in a second plane perpendicular tothe longitudinal axis of the implant comprises a dimension or measure 5%to 100%, or more, greater than the medial surface dimension measuretaken in the same plane. This results in large load bearing areas on thewide medial surface proximally and on the wide lateral surface distally.This also promotes self-centering of the implant in the medullary canal,avoiding varus or valgus mal-alignment.

In one embodiment of the invention, the implant is a femoral implant foruse in hip arthroplasty. In some embodiments, the implant has one, two,three, four, or more axially oriented protrusions on the anteriorsurface, posterior surface, or both, which act, during implantation, asguide rails. In some embodiments, there are relatively medial andlateral guide rails on the anterior and posterior surfaces. In someembodiments of the invention, the medial guide rail extends furtherdistally than the lateral guide rail, the lateral guide rail extendsfurther distally than the medial guide rail, or they can extend thesubstantially same distance. The guide rails can serve multiplepurposes. They help guide the implant during insertion, prevent rotationof the implant during and after insertion, and provide spaces betweenthe rails for compacted cancellous bone, which increases the stabilityof the inserted implant. In another embodiment of the femoral implant,there are one, two, three or more voids on the proximal portion of theimplant on the anterior surface, posterior surface, or both. These voidsmay be round, or any appropriate shape. The voids accommodate compressedcancellous bone during insertion or accommodate bone cement dispensed toassist fixation of the implant. In other embodiments, there are novoids.

In a further embodiment of the femoral implant, there is a lateral keel.Where the lateral keel arises on the proximal portion of the implant,there is a localized reduction in the cross section of the implant, whencompared to adjacent sections of the keel laterally and stem medially.This allows minimized displacement of cancellous bone during insertion,reducing forces during insertion and also resists rotation of theimplant both during and after insertion. In other embodiments, there isno lateral keel, or a keel without localized reduced cross section ofthe implant. In some embodiments, the length of the femoral implant is100 to 130 mm. In other embodiments, it may be less than 100 mm or morethan 130 mm.

In a further embodiment, the implant is a humeral implant for use inshoulder arthroplasty. In some embodiments, the implant has one, two,three, four or more stabilization ribs which provide mechanicalstructure, resist rotation of the implant within the bone, and enhancestability of the implant within the bone after implantation. In someembodiments, the ribs are on the anterior surface, posterior surface, oranterior and posterior surfaces. In other embodiments, there is astabilization fin on the lateral aspect of the proximal surface. In someembodiments of the invention, the implant includes a collar proximallyto rest on the cortical bone and prevent subsidence of the implant intothe humerus after implantation. In other embodiments, there is nocollar. In some embodiments the implant has an overall length of 70 to90 mm. In other embodiments, the implant has a length less than 70 mm,preferably about 60 mm. In some embodiments of the invention, the medialand lateral surfaces of the implant are curved, e.g., arcuatelongitudinally. In other embodiments, the medial surface is arcuate,while the lateral surface is straight, or having an axis that isparallel or substantially parallel to a central longitudinal axis of theimplant. In still other embodiments, neither the medial nor lateralsurface is curved, e.g., arcuate along the length of the implant.

In accordance with a further aspect, there is provided an implantcomprising a first end, a second end comprising a distal tip, e.g., ablunt distal tip, and disposed between the first and second ends, a stemcomprising an anterior surface, a posterior surface, a medial surface,and a lateral surface, wherein either or both of a measure or dimensionof the medial surface and a measure of the lateral surface taken in aplane substantially perpendicular to the longitudinal axis of theimplant change from proximal to distal, such that a ratio of the medialmeasure to the lateral measure changes from proximal to distal along thelongitudinal axis of the implant.

In some embodiments, the width of the medial surface and width of thelateral surface change continuously along the length of the stem. Inother embodiments, the change is not continuous.

In some embodiments, the measure of the medial surface taken in a planesubstantially perpendicular to the longitudinal axis of the implantgenerally decreases from proximal to distal along the stem and themeasure of the lateral surface taken in a plane substantiallyperpendicular to the longitudinal axis of the implant generallyincreases from proximal to distal along the stem.

In some embodiments, the entire stem portion, or a portion thereof, iscoated with a porous material for aiding in the fixation of the stem inthe long bone for a press fit implant. In other embodiments, the implantis designed for cement fixation and can have a smooth surface or aroughened, textured surface.

In accordance with a further embodiment, there is provided a method forimplanting a stem in a long bone during joint arthroplasty. The methodcomprises identifying a patient having identifying a patient having adiseased joint, surgically exposing the joint surface, excising anarticulating portion of a long bone, preparing a proximal portion of thelong bone to receive an implant, implanting a stem into the proximalportion and intramedullary canal of the long bone, said stem comprisinga medial, a lateral, an anterior, and a posterior surface, the surfacescomprising a geometry such that the ratio of medial surface measure tolateral surface measure taken in a plane substantially perpendicular tothe longitudinal axis of the stem changes along the stem from proximalto distal

The method may additionally comprise the step of securing the implantusing bone cement, such as polymethylmethacrylate (PMMA) or a compatiblefixation material. Alternatively, the implant can be press-fit.

Another aspect of the invention features a minimal incision shoulderarthroplasty technique that allows replacement of the glenoid surfaceand humeral head with only a small incision and less extensive softtissue stripping. The “mini-incision” procedure also leaves thepectoralis tendon and the majority of the inferior capsule intact. Theadvantages of the “mini-incision” procedure include a shorter incisionwith less scarring, increased safety, and a more simple exposure of theglenoid, thus allowing general orthopedists to perform a shoulderreplacement with less difficulty and potentially fewer complications.The skin incision is preferably less than 10 cm. in length, morepreferably between 7 and 10 cm.

Further features and advantages will become apparent to those of skillin the art in view of the detailed description of embodiments whichfollows, when considered together with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an anterior surface view of an implant device for implantationin the humerus.

FIG. 2 is an anterior surface view of an implant device for implantationin the femur.

FIG. 3 is an anteromedial surface view of a long bone implant.

FIG. 4 is a medial surface view of a long bone implant.

FIG. 5 is a view of a femoral implant with varus mal-alignment.

FIG. 6 is a view of a humeral implant placed in varus mal-alignment.

FIG. 7 is a view of a femoral implant placed in valgus mal-alignmentwith associated peri-prosthetic femur fracture.

FIG. 8 is an anterior surface view of a femoral implant showing thevarying width of the medial surface from proximal to distal along thestem.

FIG. 9 is an anterior surface view of a femoral implant showing thevarying width of the lateral surface from proximal to distal along thestem.

FIG. 10A-10I are schematic cross sectional areas (not necessarily toscale) of a femoral implant at approximately 10 mm intervals from afirst end of the implant to a second end of the implant.

FIG. 11 is an anterior view of a femoral implant showing guide railsalong the anterior surface of the implant.

FIG. 12 is an anterolateral view of a femoral implant showing guiderails along the anterior surface.

FIG. 13 is an anterior view of a femoral implant showing voids disposedin the proximal portion of the implant and a secondary keel feature inthe lateral proximal portion of the implant.

FIG. 13A is a cross-sectional view of the proximal section of theimplant of FIG. 13 showing the secondary keel feature.

FIG. 14 is another view of the femoral implant of FIG. 13 showing thevoids in the proximal portion and the lateral keel.

FIG. 15 is an anterolateral view of a humeral implant also showingstabilizing fins and arcuate medial and lateral surfaces.

FIG. 16 is an anteromedial view of a humeral implant showing stabilizingfins and arcuate medial and lateral surfaces.

FIGS. 17A-17F are schematic cross sectional areas (not necessarily toscale) of a humeral implant from a first, e.g., proximal end to asecond, e.g., distal end of the implant at approximately 10 mmintervals.

FIG. 18 is an image of a humeral implant placed within the bone.

FIG. 19 is an anteromedial view of a humeral implant showing asupplemental stabilization fin.

FIG. 20 is an anterolateral view of a humeral implant showing asupplemental stabilization fin.

FIG. 21 is an anterior view of a humeral implant showing an arcuatemedial surface and straight lateral surface.

FIG. 22 is another view of a humeral implant showing an arcuate medialsurface and straight lateral surface.

DETAILED DESCRIPTION

Referring now to FIGS. 1 and 2, these figures illustrate current implantdevices for implantation in humeral and femoral bones respectively.Implants used in the humerus (100) during joint arthroplasty have aproximal region (101) and a stem portion (102), the distal portionterminating in a distal tip (103). The proximal portion of the humeralimplant may have flanges (104) protruding radially from the proximalstem region, these flanges being disposed in a manner to resist rotationof the implant within the cancellous bone after implantation within thehumerus. The proximal portion will further have a receiving feature(105) for the purpose of mechanically coupling to an articulatingcomponent of the joint replacement system. Humeral stem implants willtypically have a flange feature (106) intended to restrict thepenetration of the implant within the native bone and to resistpost-operative subsidence of the implant under anatomical loadingconditions. Humeral stem implants are typically 120 mm to 160 mm inlength and femoral stems are typically in the range of 150 mm to 200 mmin length.

Implants used in the femur during joint arthroplasty are of a similarconstruct to those used in humeral joint arthroplasty. Referring to FIG.2 the implant (200) has a distal region (202), a blunt distal tip (203),a proximal region (201), and a coupling means (205) to receive anarticulating surface component. The proximal region (201) may havevarious features or surface treatments (204) thereon for the purpose ofimproving torsional stability of the implant within the bone afterimplantation. The implant may or may not also have a medial collar (206)proximally to rest on cortical bone and prevent subsidence of theimplant.

Referring now to FIGS. 3 and 4, all long bone implants can be generallydescribed as having a medial surface (307), a lateral surface (308) ananterior surface (309) and a posterior surface (310), these surfacescorresponding to the orientation of the implant within the bone afterimplantation.

In the implants currently available or disclosed within prior art theproportionate relationship between the medial surface and the lateralsurface is generally constant; at any distance along the stem, themedial surface being greater than that of the lateral surface, orvice-versa.

The surgical technique associated with these stems in both humeral andfemoral applications is generally similar, irrespective of the implantdesign; the joint structure is surgically exposed through an incisionthat is generally 120 mm to 200 mm in length, the spherical component ofthe long bone is resected and removed from the joint, a cavity isprepared within the long bone to receive the stem implant by removingnative cancellous bone from within the bone by drilling and broaching,and the stem implant is fitted within the long bone. The distal portionof the implant extends through and within the intramedullary canal ofthe bone; the proximal portion is embedded within cancellous tissue atthe proximal aspect of the bone. The implant may be secured by pressfitting within the native bone, by the application of bone cements, orby other secondary fastening means.

The final position and orientation of the implant device is at bestvariable, being subject to influences of the surgeon's skill, the accessto the bony structures available through the surgical incision, thetrajectory established by the drilling and broaching steps in theprocedure, native anomalies of the bone structure, and the patient'sgeneral anatomy.

As a consequence of this variability, it is not unusual to have implantsthat are in sub-optimal or compromising positions. Mal-position of theimplant may lead to adverse clinical outcomes, including loosening ofthe implant, post-operative mechanical instability of the joint,overstuffing of the joint, or peri-prosthetic fracture of the boneduring or after surgery.

Referring now to FIG. 5, a femoral implant is shown located within thefemur; the proximal portion of the implant (501) has a medial bias whilethe distal portion of the implant (502) has a lateral bias. This isknown as varus mal-alignment. In this position the implant devicetransfers anatomic loads (F) through the implant and couples these loadsto the native bone disproportionately at the proximal medial position(503) and the distal lateral position (504) and effectively induces acantilever effect which concentrates forces at the distal region (504).These forces may cause peri-prosthetic fractures of the bone in thedistal region of the implant (504).

Similarly, now referring to FIG. 6, a humeral implant (601) has beenmal-positioned in a similar varus manner, with which results inoverstuffing of the joint (610) and an increased risk of peri-prostheticfracture at the distal lateral region (604).

Referring to FIG. 7, a femoral implant is shown located within thefemur. The proximal portion of the implant (701) has a lateral bias andthe distal portion of the implant (702) has a medial bias. This is knownas valgus mal-alignment of the implant. Loads are disproportionatelyborne at the proximal lateral position (706) and distal medial position(704) of the bone. Further shown here is a peri-prosthetic fracture(705) of the femur which has resulted from forces (F) beinginappropriately communicated to the medial aspect of the distal tip ofthe implant (704) and therefrom through the femur bone resulting in afracture.

There remains a need for an implant device which can be implanted withinlong bone structures during joint arthroplasty which eliminates thevariability of positioning, reduces the surgical variability, and isless invasive and less traumatic to the patient.

Referring then to FIGS. 8 and 9, there is disclosed one embodiment of afemoral implant stem (800) for use in hip joint arthroplasty, theimplant having a proximal portion (809), a distal portion (802), amedial surface (803), a lateral surface (804), an anterior surface(801), a posterior surface (805) and a coupling feature (806) adjacentto the neck of the implant for receiving the articulating element of ajoint arthroplasty system.

The implant stem (800) has a first, longitudinal axis. The first, e.g.,medial surface (803) has an axial dimension, such as a width, largerthan that of an axial dimension of the second, e.g., lateral surface inthe proximal region of the stem along a second axis transverse to thelongitudinal axis and which in some embodiments is generallycontinuously decreasing in dimension (e.g., width) from the proximal end(803) to the distal end (810) of the implant (in other words, along thelongitudinal axis of the stem (800)) and a lateral surface (804) at thedistal end which has an axial dimension (e.g., width) which is largerthan that of an axial dimension of the medial surface in the distalregion of the stem and which is generally increasing in dimension (e.g.,width) from the proximal (809) to the distal end (809). In someembodiments, the axial dimension of the medial surface (803) in a planetransverse to the longitudinal axis of the stem in the proximal regionof the stem is at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%,50%, 75%, 100%, or more greater than a corresponding axial dimension ofthe lateral surface in the proximal region of the stem along an axistransverse to the longitudinal axis of the stem in the proximal regionof the stem in the same plane. The axial dimension of the lateralsurface (804) in a plane transverse to the longitudinal axis of the stemthe distal region of the stem can, in some cases, be at least about 5%,10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, 75%, 100%, or more greater thanthe axial dimension of the medial surface in the distal region of thestem transverse to the longitudinal axis of the stem in the distalregion of the stem in the same plane. In some embodiments, the axialdimension of the medial surface (803) with respect to the axialdimension of the lateral surface (804) at a given first cross-sectionallevel (e.g., through a proximal, central, or distal section of the stem(800)) defined by an axis transverse to the longitudinal axis of thestem (800) comprises a first ratio or fraction. The axial dimension ofthe medial surface (803) with respect to the axial dimension of thelateral surface (804) at a given second cross-sectional level (e.g.,through a proximal, central, or distal section of the stem) defined byan axis transverse to the longitudinal axis of the stem (800) comprisesa second ratio or fraction. The first ratio or fraction can be, forexample, at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%,100%, 125%, 150%, 200%, 300%, or more of the second ratio or fraction.This results in an implant construct which has a large load bearingsurface area on the medial surface (803) in the proximal region of thestem implant and a large load bearing surface area on the lateralsurface of the distal region of the implant (802). Further, thisconstruct produces an implant where the lateral surface dimension (e.g.,width) of the proximal region (809) is relatively small when compared tothat of the corresponding medial surface width (803), and the medialsurface dimension of the distal region (810) is substantially smallerthan that of the corresponding lateral surface dimension (802).

As a consequence of these medial to lateral surface area transitions,the implant may potentially be inserted into the native bone without theneed for drilling or reaming prior to insertion. In addition, thisconstruct effectively self-centers the implant within the intramedullarycanal of the native bone, substantially reducing the risk of varus orvalgus mal-positioning.

The embodiment illustrated in FIGS. 8 and 9 has a length in the rangeof, for example, about 100 mm to about 130 mm.

FIGS. 10a through 10i illustrates the continuously changing crosssectional area (900) and the differences in dimension, e.g., width ofthe medial (902) and lateral surfaces (901) of the femoral implant(905), the illustrated cross sections being shown at even increments ofapproximately 10 mm measured from the proximal end (FIG. 10a ) to thedistal end (FIG. 10i ) respectively. In some embodiments asschematically illustrated, the ratio of medial (902) surface dimensionto lateral (901) surface dimension at a particular transversecross-section of the stem changes from a first, e.g., proximal or distalportion (e.g., FIG. 10a ) of the stem to a second, e.g., proximal ordistal portion (e.g., FIG. 10i ) of the stem. In some embodiments, theratio of medial (902) surface dimension to lateral (901) surfacedimension (e.g., FIG. 10a ) is greater than 1:1, such as greater than1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.75:1, 2:1, 2.5:1. 3:1, 4:1, 5:1,6:1, 7:1, 8:1, 9:1, 10:1, or more, while the ratio of medial (902)surface dimension to lateral (901) surface dimension (e.g., FIG. 10i )is less than 1:1, such as less than 0.9:1, 0.8:1, 0.7:1, 0.6:1, 0.5:1,0.4:1, 0.3:1, 0.2:1 or less. In some embodiments, the ratio of medial(902) surface dimension to lateral (901) surface dimension changes(e.g., increases or decreases) by at least about 5%, 10%, 15%, 20%, 25%,30%, 35%, 40%, 45%, 50%, 60%, 70%, 75%, 80%, 90%, 100%, 150%, 200%,250%, 300%, 350%, 400%, 450%, 500%, 600%, 700%, 800%, 900%, 1000%, ormore, or increases by at least 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10×, 12×,14×, 16×, 18×, 20×, 25×, or more with respect to two differenttransverse cross sections spaced longitudinally 10 mm, 20 mm, 30 mm, 40mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, or more apart from eachother, or spaced longitudinally by 10%, 20%, 30%, 40%, 50%, 60%, 70%,80%, 90%, or more of the entire axial length of the implant, ortransverse cross sections taken at the two ends of the implant. In someembodiments, the medial (902) surface dimension is greater than thelateral (901) surface dimension at the proximal end of the implant whilethe medial (902) surface dimension is smaller than the lateral (901)surface dimension at the distal end of the implant, or vice versa.However, in some embodiments the absolute medial (902) surface dimensionis larger (or smaller) than the lateral (901) surface dimension atcross-sections throughout the axial length of the stem, while the ratioof medial (902) surface dimension to lateral (901) surface dimensionchanges with respect to at least two, three, or more differenttransverse cross sections.

FIG. 11 and FIG. 12 are an alternate embodiment of the femoral implantpreviously described, having one, two, three, four, or more supplementalgenerally axially-oriented guide rails (920) (921) located on theanterior and posterior surfaces of the implant, these guide rails (920)(921) disposed to provide supplemental centering and trajectory controlof the implant during the final insertion within the proximal bone ofthe femur. The supplemental guide rails shown are positive protrusionslocated on the anterior and posterior surfaces of the proximal region ofthe implant, the medial rail (920) extending further distally than thelateral guide rail (921) such that the distal ends of the guide rails(922 and 923) engage cancellous bone sequentially as the implant isinserted into the native bone so as to assist in continuous guidance ofthe implant during the insertion of the implant. During the finalinsertion of the implant within the bone, cancellous bone tissue iscompacted in the spaces between each of the guide rails (940 and 950) soas to increase the stability of the implant in the inserted position.

Referring now to FIG. 13 and FIG. 14, yet another embodiment of thefemoral implant is described. The anterior and posterior surfaces of theproximal region of the implant have therein one, two, three, four, ormore voids (980) disposed to accommodate compressed cancellous bonedisplaced during the insertion of the implant or to accommodate bonecement dispensed to assist fixation of the implant within the bone.Further illustrated is a secondary keel feature (990), disposed tosubstantially reduce the cross section of the lateral aspect of theimplant locally in the proximal region so as to minimize thedisplacement of cancellous bone, thereby reducing insertion forces, andto minimize the tendency to introduce a medial turning moment during thefinal insertion. FIG. 13a is a cross section through the proximal regionof the implant showing the reduced cross sectional dimension at thesecondary keel (990) relative to, for example, the dimension of themedial surface (902) of the implant, the dimension at the secondary keel(990) being at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, or lesswith respect to the dimension of the medial surface (902).

Referring now specifically to FIG. 15 and FIG. 16, another embodiment ofa stem for use in humeral applications in shoulder joint arthroplasty isdescribed. The implant (1000) is similar in construction principle tothat previously described for the femoral stem, the stem having aproximal region (1210), a distal region (1220), a receiving means (e.g.,a cavity, threaded region, complementary interlocking connector, joint,and the like) (1020) to accept an articulating element of a jointarthroplasty system, one, two, or more proximal flanges (1010) disposedto prevent subsidence of the implant stem into the cancellous bone afterimplantation, and one or a series of stabilization ribs (1120, 1100, and1110) disposed to provide mechanical structure, resist rotation of theimplant within the bone, and enhance the stability of the implant withinthe bone after implantation. The implant shown herein has an overalllength of 70 mm to 90 mm.

The medial to lateral surface dimension relationship of the humeralimplant can be similar to that previously described in detail for thefemoral implant; the axial dimension (e.g., width) of the medial surface(1070) in the proximal region (1210) is substantially wider than thedimension, (e.g., width) of the corresponding lateral surface (1060)such that the axial dimension of the medial surface (1070) in theproximal region (1210) is at least about 5%, 10%, 15%, 20%, 25%, 30%,35%, 40%, 50%, 75%, 100%, 200%, 300%, 400%, 500%, 600%, 700%, or moregreater than the axial dimension of the corresponding lateral surface(1060) on an axis transverse to the longitudinal axis of the stem thatincludes the medial surface (1070). The width of the lateral surface(1050) in the distal region is substantially wider than that of thecorresponding medial surface (1080), such that the axial dimension ofthe lateral surface (1050) in the distal region is at least about 5%,10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, 75%, 100%, 200%, 300%, 400%,500%, 600%, 700%, or more greater than the axial dimension of thecorresponding medial surface (1080) on an axis transverse to thelongitudinal axis of the stem that includes the lateral surface (1050).In some embodiments, the ratio of medial (902) surface dimension tolateral (901) surface dimension changes (e.g., increases or decreases)by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%,70%, 75%, 80%, 90%, 100%, 150%, 200%, 250%, 300%, 350%, 400%, 450%,500%, 600%, 700%, 800%, 900%, 1000%, or more, or increases by at least2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10×, 12×, 14×, 16×, 18×, 20×, 25×, ormore with respect to two different transverse cross sections spacedlongitudinally 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm,90 mm, 100 mm, or more apart from each other, or spaced longitudinallyby 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or more of the entireaxial length of the implant, or transverse cross sections taken at thetwo ends of the implant. FIGS. 17a to 17f illustrate the relativedimensions, e.g., widths of the lateral surface (1050) and the medialsurface (1080), the figures represent transverse cross sections acrossthe implant device progressing at 10 mm increments from the proximal endof the implant device (1000) to the distal end of the device. Furtherillustrated is the change in the origin of the included angle (A)between the anterior and posterior surfaces of the implant device fromlateral to medial, or vice versa as shown by the transition of the baseof a triangle formed by the included angle from the medial surface 1050of the implant device in FIG. 17a to the lateral surface 1050 of theimplant device in FIG. 17f . As illustrated, the angle A could changefrom positive to negative or negative to positive in successivecross-sections in a first direction to a second direction, and be, forexample, less than about 80, 70, 60, 50, 40, 30, 20, 10, or less degreesin a first, e.g., proximal region of the implant and greater than about20, 30, 40, 50, 60, 70, 80, or more degrees in a second, e.g., distalregion of the implant. The below table lists one example of transversedimensions at various cross-sectional levels as illustrated in FIGS.17a-17f :

Medial:Lateral Lateral Surface Medial Surface Surface FIG. Dimension(mm) Dimension (mm) Dimension Ratio 17a 1.0 6.0 6:1 17b 2.0 5.0 5:2 17c3.0 4.5 3:2 17d 3.5 3.5 1:1 17e 4.5 2.5 5:9 17f 7.0 2.5  5:14

Further shown in FIG. 15 and FIG. 16 are one or a series of stabilizingfins (1100, 1110, 1120) protruding from the anterior and/or posteriorsurfaces of the implant device. During the insertion of the proximalaspect of the implant (1210) said fins engage the soft cancellous bonetissue and compress it within the interspaces between the stabilizingfins thereby enhancing the stability within the bone, reducing thepropensity to subside post operatively and improving the rotationalstability of the implant within the native bone.

Of further note is the arcuate nature of the medial and lateral surfaces(1070 and 1060 respectively). Referring now to FIG. 18, a radiographicimage of one embodiment located within a humeral bone (1500) describedin FIGS. 15, 16 and 17 (a-f) inclusive can be seen. The arcuate medial(1060) and lateral (1070) surfaces are shown engaging the intramedullarychannel (1600). The larger medial surface (1070) is shown engaging thecortical bone at the medial aspect of the humerus in the proximal regionwhile the wider lateral surface (1060) is shown engaging the corticalbone distally.

Referring now to FIGS. 19 and 20, an alternate embodiment of the humeralimplant device previously described is shown. The humeral implant has asupplemental stabilization fin (1800) located, for example, at thelateral aspect of the proximal surface. Fin (1800) is disposed tofurther enhance the mechanical stability of the final implant within thebone and resist torsional loads on the implant to bone interface.

FIGS. 21 and 22 are alternate embodiments of a humeral stem having ancurved, e.g., arcuate medial surface (1070) and a straight lateralsurface (1060).

Although certain embodiments of the disclosure have been described indetail, certain variations and modifications will be apparent to thoseskilled in the art, including embodiments that do not provide all thefeatures and benefits described herein. It will be understood by thoseskilled in the art that the present disclosure extends beyond thespecifically disclosed embodiments to other alternative or additionalembodiments and/or uses and obvious modifications and equivalentsthereof. Certain embodiments of humeral implants as described, forexample, in U.S. patent application Ser. No. 13/088,976 to Gunther filedon Apr. 18, 2011 and glenoid implants described, for example, in U.S.Pat. Pub. No. 2010/0249938 to Gunther et al., both of which are herebyincorporated by reference in their entireties, can be used or modifiedfor use with stem embodiments as described herein In addition, while anumber of variations have been shown and described in varying detail,other modifications, which are within the scope of the presentdisclosure, will be readily apparent to those of skill in the art basedupon this disclosure. It is also contemplated that various combinationsor subcombinations of the specific features and aspects of theembodiments may be made and still fall within the scope of the presentdisclosure. For example, while the features and embodiments shown hereinhave been described in the context of applications specific toindividual bone structures, the various features described can be usedindividually, or in combination, to produce prosthetic bone implants foruse in multiple and varied skeletal applications. Accordingly, it shouldbe understood that various features and aspects of the disclosedembodiments can be combined with or substituted for one another in orderto form varying modes of the present disclosure. Thus, it is intendedthat the scope of the present disclosure herein disclosed should not belimited by the particular disclosed embodiments described above. For allof the embodiments described above, the steps of any methods need not beperformed sequentially.

What is claimed is:
 1. An implant for use in a long bone during jointarthroplasty, said implant comprising: a first end; a second endcomprising a blunt tip; and a stem of the implant disposed between thefirst and second ends, wherein a proximal portion of the stem comprisesan anterior surface, a posterior surface, a medial surface and a lateralsurface, wherein a dimension of said medial surface taken in a firstplane substantially perpendicular to the longitudinal axis of theimplant is greater than a dimension of said lateral surface taken in thesame first plane, and a distal portion of the stem comprises an anteriorsurface, a posterior surface, a medial surface, and a lateral surface,wherein a dimension of said lateral surface taken in a second planesubstantially perpendicular to the longitudinal axis of the implant, thesecond plane spaced distally apart from the first plane is greater thana dimension of the medial surface taken in the same second plane.
 2. Theimplant of claim 1, wherein the medial surface dimension taken in thefirst plane is at least 5% greater than the lateral surface dimension inthe first plane and the lateral surface dimension taken in the secondplane is at least 5% greater than the medial surface dimension taken inthe same second plane.
 3. The implant of claim 1, wherein said implantis a femoral implant.
 4. The implant of claim 3, where the proximalportion of the stem further comprises a keel arising from the lateralsurface of the stem, the medial origin of the keel comprising a sectionnarrower in an anterior to posterior measurement than adjacent sectionsof the stem medially and the keel laterally to said medial originsection.
 5. The implant of claim 3, where said implant further comprisesat least one axially oriented longitudinal protrusion on the anteriorand posterior surfaces of the proximal portion of the stem.
 6. Theimplant of claim 5, where said stem further comprises at least twoprotrusions, one relatively medial and one relatively lateral, disposedalong the longitudinal axis on the anterior and posterior surfaces ofthe proximal portion of the stem.
 7. The implant of claim 6, wherein themedial protrusion extends further distally on the stem than the lateralprotrusion extends distally.
 8. The implant of claim 1, where saidimplant is a humeral implant.
 9. The implant of claim 8, where saidimplant further comprises a proximal collar disposed between the firstend and the stem portion of the implant.
 10. The implant of claim 8,further comprising at least one anterior or posterior protrusiondisposed along the proximal portion of the stem.
 11. The implant ofclaim 8, where the stem further comprises a curved medial surface and acurved lateral surface along the length of the stem.
 12. The implant ofclaim 8, where the stem further a curved medial surface and asubstantially straight lateral surface along the length of the stem. 13.An implant for use in a long bone during joint arthroplasty, saidimplant comprising: a first end; a second end comprising a blunt distaltip; and a stem disposed between the first and second ends, said stemcomprising an anterior surface, a posterior surface, a medial surfacehaving a transverse dimension, and a lateral surface having a transversedimension, the stem having a first medial:lateral dimension ratiodefined by the transverse dimension of the medial surface taken in afirst plane with respect to the transverse dimension of the lateralsurface taken in the first plane, the stem also having a secondmedial:lateral dimension ratio defined by the transverse dimension ofthe medial surface taken in a second plane with respect to thetransverse dimension of the lateral surface taken in the second plane,wherein the first plane is substantially transverse to a longitudinalaxis of the implant, the first plane being near the first end of theimplant and wherein the second plane is substantially transverse to thelongitudinal axis of the implant, the second plane being near the secondend of the implant, wherein the second medial:lateral dimension ratio isdifferent than the first medial:lateral dimension ratio.
 14. The stem ofclaim 13, wherein the second medial:lateral dimension ratio is at leastabout 10% less than the first medial:lateral dimension ratio.
 15. Amethod of treating a patient, comprising the steps of: identifying apatient having a joint for replacement; surgically exposing the jointsurface; excising an articulating portion of a long bone; preparing aproximal portion of the long bone to receive an implant; and implantinga stem into the proximal portion and intramedullary canal of the longbone, said stem comprising a medial, a lateral, an anterior, and aposterior surface, the surfaces comprising a geometry such that theratio of medial surface transverse dimension to lateral surfacetransverse dimension taken in a plane substantially perpendicular to thelongitudinal axis of the stem changes along the axial length of the stemfrom the proximal end of the stem to the distal end of the stem.
 16. Themethod of treating a patient as in claim 16, wherein said joint is theshoulder and said long bone is the humerus.
 17. The method of treating apatient as in claim 17, additionally comprising the step of accessingthe humerus via an incision no more than about 10 cm. in length.
 18. Themethod of treating a patient as in claim 16, wherein said joint is thehip and said long bone is the femur.
 19. The method of treating apatient as in claim 16, wherein the proximal portion of the long bone isprepared to receive an implant without reaming or drilling.